2.4.- Bioreactor and operational conditions
Bioreactor cell cultures were run in a 2-L Biostat Bplus (Sartorius Stedim Biotech). The bioreactor was equipped with the necessary probes to maintain the desired culture conditions regarding pH, pO2 and temperature, stirred with two marine impellers at 60 rpm. Dissolved oxygen (DO) concentration was measured with an optical probe (VisiFerm DO, Hamilton). DO was set at 40% of saturation with a constant aeration inflow of 0.20 L/min, with variable composition controlled by a gas mix air/oxygen station. pH was measured with a standard electrode (EASYFERM PLUS, Hamilton) and maintained at 7.1 through addition of NaOH 0.5 M solution when buffer capacity was not enough to compensate culture acidification. CO2 inlet gas enrichment was fixed at 5% during the entire culture. Temperature was set at 37 ÂșC.